1. Field of the Invention
The present invention relates to a thermally assisted magnetic head for writing of signals by thermally assisted magnetic recording and to a head gimbal assembly (HGA) with this thermally assisted magnetic head, and a hard disk drive with this HGA.
2. Related Background Art
As the recording density of the hard disk drive increases, further improvement is demanded in the performance of the thin film magnetic head. The thin film magnetic head commonly used is a composite type thin film magnetic head of a structure in which a magnetic detecting element such as a magneto-resistive (MR) effect element and a magnetic recording element such as an electromagnetic coil element are stacked, and these elements are used to read and write data signals from and into a magnetic disk as a magnetic recording medium.
In general, the magnetic recording medium is a kind of a discontinuous body of fine magnetic particles aggregated, and each of the fine magnetic particles is made in a single magnetic domain structure. A recording bit is composed of a plurality of fine magnetic particles. Therefore, in order to increase the recording density, it is necessary to decrease the size of the fine magnetic particles and thereby decrease unevenness at borders of recording bits. However, the decrease in the size of the fine magnetic particles raises the problem of degradation of thermostability of magnetization due to decrease of volume.
A measure of the thermostability of magnetization is given by KUV/kBT. In this case, KU represents the magnetic anisotropy energy of the fine magnetic particles, V the volume of one magnetic particle, kB the Boltzmann constant, and T absolute temperature. The decrease in the size of fine magnetic particles is nothing but decrease in V, and, without any countermeasures, the decrease in V will lead to decrease of KUV/kBT and degradation of the thermostability. A conceivable countermeasure to this problem is to increase KU at the same time, but this increase of KU will lead to increase in the coercive force of the recording medium. In contrast to it, the intensity of the writing magnetic field by the magnetic head is virtually determined by the saturation magnetic flux density of a soft magnetic material making the magnetic poles in the head. Therefore, the writing-becomes infeasible if the coercive force exceeds a tolerance determined from this limit of writing magnetic field intensity.
As a method of solving this problem of thermostability of magnetization there is the following proposal of so-called thermally assisted magnetic recording: while a magnetic material with large KU is used, heat is applied to the recording medium immediately before application of the writing magnetic field, to decrease the coercive force, and writing is performed in that state. This according is generally classified under magnetic dominant recording and optical dominant recording. In the magnetic dominant recording, the dominant of writing is an electromagnetic coil element and the radiation diameter of light is larger than the track width (recording width). On the other hand, in the optical dominant recording, the dominant of writing is a light radiating portion and the radiation diameter of light is approximately equal to the track width (recording width). Namely, the magnetic field determines the spatial resolution in the magnetic dominant recording, whereas the light determines the spatial resolution in the optical dominant recording.
Patent Documents 1-7 and Non-patent Document 1 disclose the thermally assisted magnetic head recording apparatus of this type, in the structure in which a light source such as a semiconductor laser is located at a position apart from a slider with a magnetic recording element for generating a magnetic field and in which light from this light source is guided through an optical fiber, a lens, etc. to a medium-facing surface of the slider.
Furthermore, Patent Documents 8-11 and Non-patent Document 2 disclose the thermally assisted magnetic head in which the magnetic recording element and the light source are integrated on a side surface of the slider, and the thermally assisted magnetic head in which the magnetic recording element and the light source are integrated on the medium-facing surface of the slider.
Studies have also been conducted on the magnetic heads using SIL (Solid Immersion Lens) being a high-efficiency condenser element or a plasmon probe being a near-field light generating element. Patent Document 12 discloses an apparatus with the plasmon probe at the tip of a planar waveguide.    (Patent Document 1) International Publication WO92/02931 (JP-A 6-500194)    (Patent Document 2) International Publication WO98/09284 (JP-A 2002-511176)    (Patent Document 3) Japanese Patent Application Laid-Open No. 10-162444    (Patent Document 4) International Publication WO99/53482 (JP-A 2002-512725)    (Patent Document 5) Japanese Patent Application Laid-Open No. 2000-173093    (Patent Document 6) Japanese Patent Application Laid-Open No. 2002-298302    (Patent Document 7) Japanese Patent Application Laid-Open No. 2001-255254    (Patent Document 8) Japanese Patent Application Laid-Open No. 2001-283404    (Patent Document 9) Japanese Patent Application Laid-Open No. 2001-325756    (Patent Document 10) Japanese Patent Application Laid-Open No. 2004-158067    (Patent Document 11) Japanese Patent Application Laid-Open No. 2004-303299    (Patent Document 12) U.S. Pat. No. 6,795,630    (Non-patent Document 1) Shintaro Miyanishi et al., “Near-field Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, 2005, Vol. 41, No. 10, pp 2817-2821    (Non-patent Document 2) Keiji Shono and Mitsumasa Oshiki “Status and Problems of Thermally Assisted Magnetic Recording” Journal of the Magnetics Society of Japan, 2005, Vol. 29, No. 1, pp 5-13